Foamable article

ABSTRACT

A foamable article is disclosed. The article includes a substrate and an outer layer covering at least a portion of the substrate and including an unactivated expandable sphere foaming agent and an unactivated chemical foaming agent. The unactivated foaming agents may be activated to increase the volume of the outer layer.

TECHNICAL FIELD

This invention relates to a foamable article, in particular a foamablearticle including a substrate and an outer layer covering at least aportion of the substrate and including an unactivated expandable spherefoaming agent and an unactivated chemical foaming agent.

BACKGROUND

The use of hearing protective and noise attenuating devices are wellknown, and various types of devices have been considered. Such devicesinclude earplugs and semi-aural devices partially or completelyconstructed of foam or rubber materials that are inserted into, orplaced over, the ear canal of a user to physically obstruct the passageof sound waves into the inner ear.

Compressible or “roll-down” type earplugs generally comprise acompressible, resilient body portion and may be made of suitable slowrecovery foam materials. The earplug may be inserted into the ear canalof a user by first rolling it between fingers to compress the bodyportion, then pushing the body portion into the ear canal, andsubsequently allowing the body portion to expand to fill the ear canal.

Push-in type earplugs have also been considered, and may include acompressible attenuating portion and a stiff portion that extends fromthe attenuating portion. To insert a push-in type earplug, the usergrasps the stiff portion and pushes the attenuating portion into the earcanal with an appropriate level of force. The attenuating portioncompresses as it is accommodated in the ear canal. Push-in earplugs mayallow the earplug to be quickly and easily inserted in an ear canal, andmay promote hygiene by minimizing contact with the attenuating portionof the earplug prior to insertion.

Although push-in earplugs exhibit desirable characteristics in variousapplications, they may be costly and may pose difficult manufacturingchallenges.

SUMMARY Glossary

“Mold” means a hollow form that may or may not impart a shape on acomponent placed in the hollow form.

“Thermally bonded” means a state in which molecules of two materials orsurfaces have diffused into the material or surface of the other when ina molten phase such that a bond is formed. Chemical bonding is absent ordoes not provide the primary source of bonding between thermally bondedmaterials or surfaces.

“Thermoplastic” means a polymer that can be repeatably heated andre-shaped and will retain its shape upon cooling.

“Thermoset” means a polymer that may be irreversibly cured.

“Unactivated” when referring to a foaming agent means that the foamingagent can be further activated to facilitate the formation of gas orcells in a material.

In one embodiment of the present invention, an article is disclosed,including an elongate core including a first material and having firstand second ends and an outer major surface, and an outer layer includinga second material and covering at least a portion of the outer majorsurface of the elongate core. The second material includes anunactivated expandable sphere foaming agent and an unactivated chemicalfoaming agent. The unactivated foaming agents may be activated toincrease the volume of the outer layer, and the core exhibits astiffness that is greater than a stiffness of the outer layer. In anexemplary embodiment, the second material includes between 0.5% weightand 3% weight of an unactivated chemical foaming agent, between 0.5%weight and 9.5% weight of an unactivated expandable sphere foamingagent, and between 90% and 99% by weight ofstyrene-ethylene-butylene-styrene (SEBS). In another exemplaryembodiment, a channel extends at least partially through the elongatecore between the first and second ends in a longitudinal direction. Invarious exemplary embodiments, the outer layer has an outer diameterbetween 2.5 mm and 6.5 mm, the elongate core has an outer diameterbetween 1.5 mm and 3.5 mm, and the elongate core has a length betweenthe first and second ends that is greater than 1 m.

In another embodiment of the present invention, and article isdisclosed, including a substrate including a first material and having amajor surface, and an outer layer including a second material andcovering at least a portion of the major surface of the substrate. Thesecond material includes an unactivated expandable sphere foaming agentand an unactivated chemical foaming agent. The unactivated foamingagents may be activated to increase the volume of the outer layer, andthe substrate exhibits a stiffness that is greater than a stiffness ofthe outer layer. In an exemplary embodiment, the second materialcomprises between 0.5% weight and 3% weight of an unactivated chemicalfoaming agent, between 0.5% weight and 9.5% weight of an unactivatedexpandable sphere foaming agent, and between 90% and 99% by weight ofstyrene-ethylene-butylene-styrene (SEBS).

U.S. patent application Ser. No. ______, titled Method of Making anEarplug and filed on the same date herewith, addresses a method ofmaking personal protective equipment such as a push-in earplug, and U.S.patent application Ser. No. ______, titled Push-In Earplug and filed onthe same date herewith, addresses the structure and configuration of apush-in earplug, and are incorporated herein by reference.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a push-in earplug according to thepresent invention.

FIG. 2 is a cross-sectional view of a push-in earplug according to thepresent invention.

FIGS. 3A-3D are cross-sectional views of exemplary push-in earplugsaccording to the present invention showing sound attenuating portionshaving various exemplary shapes.

FIG. 4 is a perspective view of a pre-form that includes an elongatecore and an outer layer in an intermediate state of an exemplary methodof making an earplug.

FIG. 5 is a schematic representation of an exemplary manufacturingprocess according to the present invention.

FIGS. 6A and B are cross-sectional views of an example of a mold used inan exemplary embodiment of the present invention.

FIGS. 7A and B are cross-sectional views of an example of a mold used inan exemplary embodiment of the present invention.

FIG. 8 is a schematic representation of an exemplary manufacturingprocess according to the present invention.

DETAILED DESCRIPTION

The present invention provides a foamable article, such as an articlethat may be used to make an earplug or other product. The articleincludes a substrate including a first material and having a majorsurface, and an outer layer including a second material covering atleast a portion of the major surface of the substrate. The outer layerincludes an unactivated foaming agent that may be activated to increasethe volume of the outer layer. The article may be suitable to form, forexample, an earplug that includes a relatively stiff elongate corecovered, directly or indirectly, by a relatively soft outer layer havinga compressible sound attenuating portion that may be inserted into theear canal of a user, and stem portion that may be grasped by a user tohandle the earplug. Such an earplug may be easily inserted into an earcanal without first requiring that the sound attenuating portion becompressed or “rolled down.” The present invention may minimizedifficult and expensive manufacturing techniques associated with formingearplugs, other personal protective equipment, and other devices andcomponents.

FIGS. 1 and 2 show a push-in earplug 100 according to the presentdescription. Earplug 100 includes an elongate core 110 made of a firstmaterial and having first and second ends 111 and 112, and an outermajor surface 113. Earplug 100 further includes an outer layer 120 madeof a second material and bonded, directly or indirectly, to at least aportion of outer major surface 113 of elongate core 110. Outer layer 120includes a sound attenuating portion 121 for at least partial insertioninto the ear canal of a user, for example, and a stem portion 122 havinga smaller diameter and greater average density than sound attenuatingportion 121. In some embodiments, a channel 115 extends completely orpartially through elongate core 110 between first and second ends 111and 112.

During insertion of earplug 100, stem portion 122 and elongate core 110serve as a handle which may be gripped by a user. Earplug 100, andspecifically sound attenuating portion 121, is brought proximate to theuser's ear and inserted into the ear canal. Sound attenuating portion121 compresses as it is positioned, and elongate core 110 providessufficient stiffness to facilitate insertion. In use, sound attenuatingportion 121 is positioned substantially within an ear canal to block thepassage of sound and stem portion 122 extends outwardly from the earcanal to provide a handle to remove the earplug.

Elongate core 110 provides a substrate onto which outer layer 120 may becovered, directly or indirectly, and facilitates insertion of earplug100 into the ear canal of a user. In an exemplary embodiment, elongatecore 110 is made of a first material that exhibits greater rigidity orstiffness than outer layer 120, yet is soft enough to be comfortable andsafe for a user. Elongate core 110 provides sufficient rigidity thatearplug 100 may be positioned for use at least partially in the ear of auser by pushing sound attenuating portion 121 into the ear canal with anappropriate force. That is, a sufficiently stiff elongate core 110combined with an appropriate outer layer 120 allows earplug 100 to bepositioned for use at least partially in the ear of a user without theneed to first compress or “roll down” sound attenuating portion 121.Direct insertion without the need to first compress or “roll down” soundattenuating portion 121, for example, promotes hygiene by limitingcontact with sound attenuating portion 121 prior to placement in theear. Elongate core 110 also exhibits an appropriate level of flexibilitysuch that it may slightly deform to the contours of the ear canal whenpositioned for use.

Elongate core 110 is made from one or more materials that can suitablybond to, and are otherwise compatible with, the material of outer layer120 or one or more intermediate layers. In an exemplary embodiment,elongate core 110 is made from a blend of polypropylene andstyrene-ethylene-butylene-styrene (SEBS), such as TUFPRENE availablefrom S&E Specialty Polymers, LLC. of Lunenburg, Mass. Other suitablematerials include SANTOPRENE 101-90, available from Exxon MobileCorporation, and other materials exhibiting appropriate stiffness suchthat attenuating portion 121 of earplug 100 may be easily inserted intothe ear canal of a user.

Elongate core 110 may be made of one or more materials having aspecified hardness. In various exemplary embodiments, the hardness of atleast a portion of elongate core 110 is between 50 and 100 Shore A, orbetween 70 and 90 Shore A, or about 80 Shore A. A desired hardness maydepend on the dimensions of elongate core 110 such that elongate core110 exhibits a desired stiffness.

In an exemplary embodiment, elongate core 110 has a circularcross-section that is substantially uniform at any location betweenfirst and second ends 111 and 112 such that elongate core 110 exhibits agenerally cylindrical shape. A circular cross section may minimize edgesthat may cause discomfort by contacting portions of a user's ear. Invarious other exemplary embodiments, elongate core may have atriangular, square, or other suitable cross-section, or may have across-section that varies along the length of earplug 100. Outer majorsurface 113 may have a knurled, grooved, or otherwise textured surface.Such a surface may increase the surface area that contacts outer layer120 or an intermediate layer such that a robust bond is created. In someexemplary embodiments, elongate core 110 includes multiple concentriclayers, such as a layer to provide a desired stiffness and a layer thatfacilitates a robust bond with the outer layer, or that provides otherdesired characteristics.

In some exemplary embodiments, elongate core 110 is hollow and in theform of a tube defining a channel 115. Earplug 100 having a hollowelongate core 110 may be manufactured such that components of a receiveror of a communication system may be attached to the earplug.Alternatively or in addition, channel 115 may accommodate one or morefilters or other passive hearing elements to provide an attenuationcurve having a desired shape. For example, filters positioned in channel115 may cause nonlinear attenuation of high level impulses produced byexplosions, gunfire, or the like. Channel 115 may also provide a recessthat a cord may be attached to, such that first and second earplugs maybe joined, or that ends of a headband may be attached to in a semi-auralhearing protector.

Earplug 100 further includes an outer layer 120 substantially covering,directly or indirectly, elongate core 110 and including soundattenuating portion 121 and stem portion 122. In an exemplaryembodiment, outer layer 120 substantially surrounds outer major surface113 of elongate core 110 and extends from first end 111 to second end112 of elongate core 110. In some embodiments, outer layer 120 is acontiguous layer such that portions of sound attenuating portion 121contact portions of stem portion 122. First and second ends 111 and 112of elongate core 110 may be at least partially exposed, and elongatecore 110 may be colored similarly or dissimilarly from the color ofouter layer 120 to hide or exhibit the presence of elongate core 110.Sound attenuating portion 121 is positioned near first end 111 ofelongate core 110 and is shaped to be accommodated in an ear canal of auser. In an exemplary embodiment, sound attenuating portion 121 has asubstantially domed or hemispherical shape, and has a diameter at itswidest point that is greater than a diameter of stem portion 122. Invarious other embodiments shown in FIGS. 3A through 3D, for example,sound attenuating portions 125, 126, 127, 128, respectively, may bebullet-shaped, bell-shaped, cone-shaped, mushroom-shaped, or otherwiseshaped to provide a desired fit or to suit a particular application.

Outer layer 120 is made of soft and pliable foam, rubber, polymer, orother suitable material that may be comfortably positioned in an earcanal of a user. In an exemplary embodiment, outer layer 120 is made ofan SEBS, such as MONPRENE MP1900 available from Teknor Apex ofPawtucket, R.I. Other suitable materials include plasticized polyvinylchloride, ethylene propylene diene monomer (EPDM) rubber, styrenebutadiene rubber (SBR), butyl rubber, natural rubbers, otherthermoplastics, thermoset polymers, and other suitable materials asknown in the art that can be formulated to exhibit an appropriatehardness range. In an exemplary embodiment, the materials of elongatecore 110 and outer layer 120 are selected such that the primary sourceof bonding between elongate core 110 and outer layer 120, directly orindirectly, is thermal bonding. An additional adhesive is not requiredto bond elongate core 110 and outer layer 120, and such an adhesive isnot present between elongate core 110 and outer layer 120 in anexemplary embodiment. In some exemplary embodiments, outer layer 120includes multiple concentric layers, such as a layer to provide desiredcharacteristics for contacting an ear canal of a user and a layer thatfacilitates a robust bond with the elongate core, or layers thatprovides other desired characteristics.

The material of outer layer 120 may be selected to control thefriability of the outer layer 120 such that it may not easily be brokenor disintegrate during use. The friability of an earplug may becontrolled in part by selecting a material having an appropriatemolecular weight, with higher molecular weight generally resulting in aless friable earplug. In an exemplary embodiment, outer layer 220includes an SEBS having a molecular weight between 100,000 Daltons and200,000 Daltons, as measured by gel permeation chromatography analysisas known in the art, such as according to ASTM D6474-99.

The density of outer layer 120 can be controlled during manufacturing toprovide a specified density as desired for a particular application.Outer layer 120 may exhibit a density that varies by thickness, forexample, such that outer layer 120 has an integral outer skin that ismore dense than the remainder of outer layer 120. Such a skin may bepresent on one or both of sound attenuating portion 121 and stem portion122. Alternatively, sound attenuating portion 121 or stem portion 122may have a substantially uniform density. In an exemplary embodiment,irrespective of the presence of an integral outer skin or varyingdensities within sound attenuating portion 121 or stem portion 122,sound attenuating portion 121 has a first average density ρ1 and thestem portion has a second average density ρ2. First and second averagedensities ρ1 and ρ2 can be found by averaging the densities at eachlocation of sound attenuating portion 121 or stem portion 122. Withoutbeing bound by theory, the average density is believed to provide anindication of the ability of sound attenuating portion 121 or stemportion 122 to compress or otherwise conform when subjected to anexternal force. The first average density ρ1 of sound attenuatingportion 121 is selected such that sound attenuating portion may providea comfortable fit by conforming to the ear canal of a user, whileproviding a desired level of sound attenuation. In various exemplaryembodiments, the first average density ρ1 of a sound attenuating portion121, comprising a foamed SEBS for example, is between 100 kg/m³ and 180kg/m³, or 110 kg/m³ and 160 kg/m³, or may be about 125 kg/m³. The secondaverage density ρ2 of stem portion 122 is greater than the first averagedensity ρ1, and in various exemplary embodiments is between 200 kg/m³and 300 kg/m³, 225 kg/m³ and 275 kg/m³, or may be about 250 kg/m³.Accordingly, in various exemplary embodiments, the second averagedensity ρ2 of stem portion 122 of outer layer 120 is greater than 1.2,1.5, 2 or more times the first average density ρ1 of sound attenuatingportion 121 of outer layer 120.

Earplug 100 may be formed in a multiple step process. In an exemplaryembodiment, earplug 100 is formed in a process that involves anintermediate state in which outer layer 120 is covered around elongatecore 110, directly or indirectly, to result in a pre-formed hearingprotection device such as pre-form 130, but does not yet include soundattenuating portion 121. In the intermediate state shown in FIG. 4,outer layer 120 of pre-form 130 includes an unactivated foaming agent.In an exemplary embodiment, the unactivated foaming agent includes anexpandable sphere foaming agent that includes thermoplastic spheres, forexample, that include a shell encapsulating a hydrocarbon or otherappropriate gas that expands when exposed to heat or other activationsource. Expansion of the thermoplastic shell results in an increasedvolume and reduced density of the material of outer layer 120. Theunactivated foaming agent may also be a chemical foaming agent thatincludes an expandable material that is self-contained or otherwise notcontained by an expandable sphere. Activation of such a foaming agentcauses the expandable material to expand creating voids or gaps in thematerial of the outer layer. In an exemplary embodiment, the outer layer120 of pre-form 130 includes an unactivated expandable sphere foamingagent and an unactivated chemical foaming agent. Activation of thefoaming agent or agents present in outer layer 120, and the associatedexpansion of outer layer 120, can be controlled to provide an earplug100 having a sound attenuating portion 121 and stem portion 122exhibiting a desired shape, density, hardness, and other desiredcharacteristics. The presence of both an expandable sphere foaming agentand a chemical foaming agent may assist in providing sufficientstructure and expansion such that the outer layer may be appropriatelyformed during activation, while reducing the hardness of the outer layerfrom a level that would otherwise result if only an expandable spherefoaming agent were used. Some or all of a gas generated by a chemicalfoaming agent may escape during activation such that some or all of thegas is not present in the outer layer after activation. Some or all ofan expandable sphere foaming agent may remain in the outer layer of afinal earplug such that a final earplug may include thermoplasticspheres. In an exemplary embodiment, outer layer 120 of earplug 100includes between 1% and 5% weight, and may include approximately 3%weight, of the foaming agent or remnants of the foaming agent.

In the intermediate state shown in FIG. 4, pre-form 130 may be cut tothe desired length of earplug 100, may be cut to an extended lengthsufficient for subsequent formation of many earplugs, or may remainuncut such that activation of outer layer 120 occurs prior to cutting asdescribed below with reference to FIG. 8. Pre-form 130 having anextended length may facilitate handling for subsequent processing andactivation of the foaming agent. In an exemplary embodiment, pre-form130 is cut to an extended length that can be subsequently cut andactivated to yield a desired quantity of earplugs 100. An extendedpre-form 130 may be coiled or otherwise shaped for ease in transportingor handling.

The present invention provides a method of making personal protectiveequipment, such as earplug 100 described above. An exemplary methodincludes steps of covering a substrate with an outer layer, and applyingheat to at least a portion of the outer layer such that at least aportion of the outer layer expands. Expansion of the outer layer occursdue to activation of a foaming agent present in the material of theouter layer and can be controlled by positioning at least a portion ofthe outer layer in a mold prior to expansion. Portions of the outerlayer may be confined by the shape of the mold as the outer layerexpands, or are shielded from heat to limit activation of the foamingagent.

The method described herein is suitable not only for manufacturingearplugs, but also for manufacturing other types of hearing protectiondevices and components for other personal protective equipment, as wellas other molded or formed parts suitable for other applications. Forexample, the present method provides a process for making a seal for afacepiece of a respiratory protection device that can be foamed toprovide a desired shape and density. Other exemplary applicationsinclude the manufacture of ear muffs, respirators, eyewear, otherpersonal protective equipment, components of such personal protectiveequipment, and other applications.

An exemplary method of making a push-in earplug according to the presentinvention includes the steps of covering an elongate core, directly orindirectly, with an outer layer comprising an unactivated foaming agent,and activating the foaming agent of at least a portion of the outerlayer to form a sound attenuating portion and a stem portion bonded,directly or indirectly, to the elongate core.

FIG. 5 shows a schematic of an exemplary method of making an earplug 200according to the present invention. An extended elongate core 210 isformed by extruding a first material through a first die 240 and drawingthe first material to an appropriate diameter. As described above, theelongate core may be solid or may include a longitudinal channelextending through all or a portion of elongate core 210, and may includeone or more concentric layers having differing characteristics. Thefirst material may be cooled such that it remains stable in subsequentsteps of the manufacturing process. The magnitude of temperature changemay depend on the materials used and the desired characteristics of thefinal product. In an exemplary embodiment, elongate core 210 is cooledas necessary such that it exhibits a temperature at a point before beingcovered by second die 250 that is lower than an activation or curingtemperature of outer layer 220. Prior to being covered, elongate core210 has an extended length and is not yet cut to the desired length foran earplug.

In the embodiment shown in FIG. 5, elongate core 210 is covered,directly or indirectly, with an outer layer 220 comprising a secondmaterial, by second die 250. Second die 250 may be a co-extrusion die orother suitable die as known in the art. In an exemplary embodiment, thesecond material comprises a thermoplastic and one or more unactivatedfoaming agents. Outer layer 220 is applied to elongate core 210 whileremaining at a temperature below an activation temperature of theunactivated foaming agents. In an exemplary embodiment, the secondmaterial includes SEBS and a foaming agent having an activationtemperature between 100° C. and 205° C., 120° C. and 190° C., or ofabout 170° C. Other suitable materials include plasticized polyvinylchloride, ethylene propylene diene monomer (EPDM) rubber, styrenebutadiene rubber (SBR), butyl rubber, natural rubbers, otherthermoplastics, thermoset polymers, and other suitable materials asknown in the art. In embodiments in which outer layer 220 includes asecond material having a rubber or thermoset polymer, outer layer 220may be applied at a temperature below a vulcanizing or curingtemperature of the rubber or thermoset polymer. In such an embodiment,outer layer 220 may include an unactivated foaming agent and an uncuredor partially cured rubber or thermoset polymer that can be subsequentlyactivated and cured, respectively, with heat or other suitableactivation or curing process.

The weight percentage of foaming agent in outer layer 220 when initiallyapplied to elongate core 210 may be selected based on the type ofthermoplastic or other material used and the desired final shape,density, hardness or other characteristics of sound attenuating portion221. In an exemplary embodiment, outer layer 220 has an initialcomposition of between 90% and 99.5% SEBS and between 10% and 0.5% of anappropriate unactivated foaming agent, or of approximately 93% SEBS and7% of an unactivated expandable sphere foaming agent, such as EXPANCEL930 DU 120, EXPANCEL 920 DU 120, both available from Eka Chemicals AB ofSundsvall, Sweden. In other exemplary embodiments, outer layer 220 hasan initial composition including an unactivated chemical foaming agentsuch as oxybis benzene sulfonyl hydrazide (OBSH) available from BiddleSawyer Corp. of New York, N.Y. The presence of a chemical foaming agentsuch as an OBSH foaming agent may yield a sound attenuating portionhaving a lower hardness value than a sound attenuating portion formed ofan outer layer including an expandable sphere foaming agent such asEXPANCEL as the only foaming agent. In an exemplary embodiment, outerlayer 220 includes an unactivated expandable sphere foaming agent and anunactivated chemical foaming agent. The presence of both an expandablesphere foaming agent and a chemical foaming agent may assist inproviding sufficient structure such that the outer layer may beappropriately formed and that may not be present with a chemical foamingagent alone, while reducing the hardness of the outer layer from a levelthat would otherwise result if only an expandable sphere foaming agentwere used. Accordingly, the combination of a chemical foaming agent andan expandable sphere foaming agent may result in an outer layer having ahardness level appropriate for a desired application, such as forinsertion into an ear canal. In an exemplary embodiment, outer layer 220when initially applied may include between approximately 0.5% weight and3% weight of an unactivated chemical foaming agent, or of approximately2% weight of an uactivated chemical foaming agent, and betweenapproximately 0.5% weight and 9.5% weight of an unactivated expandablesphere foaming agent, or of approximately 2% weight of an unactivatedexpandable sphere foaming agent. Outer layer 220 may also include othersuitable foaming agents, or various combinations of EXPANCEL foamingagents, OBSH foaming agents, and other suitable foaming agents. Outerlayer 220 may further include pigment to impart a desired color,antioxidants, UV stabilizers, and oils or waxes to aid in extrusion andmold release as known in the art.

In some exemplary embodiments, outer layer 220 is in a molten state whencovered over elongate core 210. As a result, molecules of outer layer220 and elongate core 210, or of one or more intermediate layers, arebelieved to diffuse into the material or surface of each other and athermal bond is formed. When the materials or surfaces cool andsolidify, outer layer 220 remains thermally bonded, directly orindirectly, to elongate core 210. In an exemplary embodiment,significant chemical bonding is absent such that the primary source ofbonding between elongate core 210 and outer layer 220 is thermalbonding. In other exemplary embodiments, outer layer 220 contactselongate core 210 or one or more intermediate layers when covered overelongate core 210 but no significant bond is formed between outer layer220 and elongate core 210 or one or more intermediate layers. Uponactivation and/or curing of outer layer 220, a thermal bond may beformed, directly or indirectly, between outer layer 220 and elongatecore 210.

In other exemplary embodiments, elongate core 210 may be covered withouter layer 220, or one or more intermediate layers, by laminating,molding, spraying, dipping, or other suitable process as known in theart as an alternative or in addition to second die 250. Such steps mayoccur before or after elongate core 210 is cut to a desired length.Regardless of the process used, the temperature of outer layer 220should remain below the activation temperature of the foaming agent(s)such that the foaming agent(s) remain unactivated during the coveringprocess. In the event that an uncured or partially cured material isincluded in outer layer 220, such as an EPDM rubber or thermosetpolymer, the temperature of outer layer 220 should remain below thecuring temperature of the material.

In an exemplary embodiment, elongate core 210 covered by outer layer 220is cut to the length of a desired earplug with cutter 260. The result ispre-form 230 having elongate core 210 and outer layer 220 in which outerlayer 220 includes an unactivated foaming agent that may be subsequentlyactivated to create an earplug having a sound attenuating portion 221and a stem portion 222.

Cutter 260 may cut pre-form 230 to a desired length of earplug 200, orto an extended length sufficient for subsequent formation of manyearplugs. In an exemplary embodiment, pre-form 230 is cut to an extendedlength that can be subsequently cut and activated, or vice versa, toyield a desired quantity of earplugs 200. An extended pre-form 230 maybe coiled or otherwise shaped for ease of handling or transportation.

In an exemplary embodiment, the unactivated foaming agent present inouter layer 220 includes thermoplastic spheres encapsulating ahydrocarbon or other expandable material. Application of an appropriateamount of heat causes the thermoplastic shell and hydrocarbon to expand.In other exemplary embodiments, the foaming agent includes, alone or incombination with an expandable sphere foaming agent, an expandablematerial that is self-contained or not otherwise encapsulated, and thatproduces gas when exposed to heat or other activation source. If leftunrestrained, activation of the foaming agent(s) creates cells in outerlayer 220, ultimately increasing volume and decreasing density of outerlayer 220. Expansion of outer layer 220 can be controlled by thethickness and composition of outer layer 220, selective application ofheat, catalyst, or other activation source, and/or by placing at least aportion of pre-form 230 in a mold to limit expansion of outer layer 220as the foaming agent is activated.

In the exemplary method shown in FIGS. 6A and 6B, mold 270 is used tocontrol expansion of outer layer 220. Mold 270 includes a first cavity271 in the form of a stem portion that receives a portion of pre-form230. Pre-form 230 may be cut to the length of a desired earplug 200prior to being placed in mold 270. Alternatively, pre-form 230 may be ofan extended length and may be cut to length after being inserted intomold 270. Cutting pre-form 230 after insertion into mold 270 mayfacilitate handling and insertion. Heat is applied to the exposedportion of pre-form 230 to raise the temperature of outer layer 220 atleast to an activation temperature of a foaming agent present in outerlayer 220 and cause outer layer 220 to expand, as shown in FIG. 6B. Theportion of earplug 200 positioned in first cavity 271 may be effectivelyshielded from heat such that activation of the foaming agent is limited.Alternatively or in addition, first cavity 271 constrains outer layer220 and substantially inhibits expansion caused by activation of thefoaming agent that would otherwise result in a greater volume and lessdense outer layer. Elongate core 210 and outer layer 220 aresubsequently cooled and ejected from mold 270. The finished earplug 200includes a sound attenuating portion 221 formed by the exposed outerlayer that could freely expand and a stem portion 222 that was partiallyconstrained in mold 270 during activation of the foaming agent. Due tothe constraint of the mold and/or limited activation of the foamingagent, stem portion 222 may have a greater average density and/or agreater hardness than that of sound attenuating portion 221.

In the exemplary embodiment of FIGS. 7A and 7B, mold 370 is used tocontrol expansion of outer layer 320 of pre-form 330. Mold 370 includesa first cavity 371 in the form of a stem portion that receives a portionof pre-form 330. Mold 370 further includes a second cavity 372 in theform of a sound attenuating portion. When pre-form 330 is initiallyplaced in mold 370, a gap 375 exists between pre-form 330 and aperimeter of second cavity 372. In some embodiments, a small gap 376 mayexist between pre-form 330 and a perimeter of first cavity 371. Uponapplication of heat or other suitable activation source, a portion ofouter layer 320 expands to fill gap 375 and substantially conforms tothe shape of second cavity 372. The portion of earplug 300 positioned infirst cavity 371 may be effectively shielded from heat such thatactivation of the foaming agent is limited. Alternatively or inaddition, expansion of outer layer 220 that would otherwise occur duringactivation of the foaming agent is constrained by first cavity 371.Further, as application of heat softens outer layer 320 and the foamingagent is activated, outer layer 320 may expand to fill first cavity 371and some of outer layer 320 initially in first cavity 371 may flow intosecond cavity 372 to fill gap 375. In an exemplary embodiment, mold 370includes small gas vents to allow excess gas to escape while preventingpassage of any molten material.

In an exemplary embodiment, mold 370 is oriented such that first cavity371 is oriented above second cavity 372 during a portion or all of theactivation process. Such an orientation may allow material to flow fromfirst cavity 371 into second cavity 372 during activation. Further, anorientation in which first cavity 371 is oriented above second cavity372 may facilitate the formation of an integral skin on soundattenuating portion 321 because cells or gaps formed during activationof the foaming agent may tend to move upward and away from a lowersurface of cavity 372.

Earplug 300 is subsequently cooled and ejected from mold 370. Finishedearplug 300 includes a sound attenuating portion 321 having the shape ofsecond cavity 372 of mold 370, and a stem portion 322 having the shapeof first cavity 371 of mold 370. Due to the constraint of first cavity371 and/or limited activation of the foaming agent in the area of firstcavity 371, stem portion 322 may have a greater average density and/orhardness than that of sound attenuating portion 321.

In the exemplary embodiment shown in FIGS. 7A and 7B, earplug 300 isformed from pre-form 330 having a total length 1 in a longitudinaldirection between approximately 15 mm and 40 mm, or of about 25.5 mm.Outer layer 320 has an outer diameter d1 between approximately 2.5 mmand 6.5 mm, or of about 4.5 mm, elongate core 310 has an outer diameterd3 between approximately 1.5 mm and 3.5 mm, or of about 2.5 mm, andchannel 315 has a diameter d4 between approximately 1.0 mm and 2.0 mm orof approximately 1.5 mm. After activation of outer layer 320 describedabove, as shown in FIG. 7B, final earplug 300 has a total length L in alongitudinal direction between approximately 15 mm and 40 mm, or ofapproximately 25.5 mm, sound attenuating portion 321 has an outerdiameter D1 at its widest point between approximately 8 mm and 16 mm, orof approximately 12.5 mm, stem portion 322 has a diameter D2 betweenapproximately 3 mm and 10 mm, or of approximately 6.5 mm, elongate core310 has an outer diameter D3 between approximately 1.5 mm and 3.5 mm, orof approximately 2.5 mm, and channel 115 has a diameter D4 betweenapproximately 1.0 mm and 2.0 mm, or of approximately 1.5 mm. Thedimensions of pre-form 330 and finished earplug 300 can be varied basedon the materials of outer layer 320 and elongate core 310, and asrequired to form a final earplug 300 having desired characteristics fora particular application.

FIG. 8 shows another exemplary method of making an earplug according tothe present invention. The method includes a step of activating afoaming agent in outer layer 420 prior to cutting the elongate core 410and outer layer 420 to a desired length. Similar to the method describedabove with reference to FIG. 5, a first material is extruded throughfirst die 440 and drawn to an appropriate diameter. The extruded anduncut elongate core 410 is cooled and covered, directly or indirectly,with outer layer 420. In an exemplary embodiment, elongate core 410 iscovered with outer layer 420 by a second die 450. Alternatively,elongate core 410 can be covered with outer layer 420 by laminating,molding, spraying, dipping or any other suitable process known in theart.

Elongate core 410 and outer layer 420 may be subsequently cooled.Portions of the uncut elongate core 410 and outer layer 420 are thenpositioned in mold 470 by, for example, bringing two halves of mold 470together over the uncut elongate core 410 and outer layer 420. With themold appropriately positioned relative to the uncut elongate core 410and outer layer 420, the foaming agent is activated by heat or otheractivation source to cause outer layer 420 to expand. In embodiments inwhich outer layer 420 includes an uncured or partially cured material,application of heat or other activation source also causes outer layer420 to cure. In an exemplary embodiment, mold 470 includes a firstcavity 471 in the form of a stem portion and a second cavity 472 in theform of a sound attenuating portion. Upon application of heat or othersuitable activation source, a portion of outer layer 420 expands to fillsecond cavity 472 and substantially conform to the shape of secondcavity 472. The portion of earplug 400 positioned in first cavity 471may be effectively shielded from heat such that activation of thefoaming agent is limited. Alternatively or in addition, expansion ofouter layer 420 that would otherwise occur during activation of thefoaming agent is substantially constrained by first cavity 471. Further,as application of heat softens outer layer 420 and the foaming agent isactivated, some of outer layer 420 initially in first cavity 471 mayflow into second cavity 472. In an exemplary embodiment, mold 470includes small gas vents to allow excess gas to escape while preventingpassage of any molten material.

Elongate core 410 and activated outer layer 420 are then cooled, removedfrom mold 470, and cut to a desired length with cutter 460 to result infinished ear plug 400. Finished earplug 400 includes a sound attenuatingportion 421 having the shape of second cavity 472, and a stem portion422. Due to the constraint of first cavity 471 and/or limited activationof the foaming agent in the area of first cavity 471, stem portion 422may have a greater average density and/or hardness than that of soundattenuating portion 421.

In another exemplary embodiment, only a portion of the uncut elongatecore 410 and outer layer 420 are positioned in a mold cavity. The moldcavity may be in the form of a stem such that expansion of a portion ofouter layer 420 is substantially constrained to form stem portion 422,while the remaining portion of outer layer 420 may freely expand to formsound attenuating portion 421. Alternatively, the mold cavity may be inthe form of a sound attenuating portion such that expansion of a portionof outer layer 420 is constrained and selectively activated to formsound attenuating portion 421, while the remaining portion of outerlayer 420 is not activated, or is only partially activated, and formsstem portion 422.

An earplug according to the present invention may also be made accordingto variations of methods described herein and other methods. Forexample, an exemplary earplug may be made by covering a relativelystiffer elongate core with an outer layer as a foaming agent isactivated, or covering a relatively stiffer elongate core with an outerlayer that has been previously foamed. The foamed outer layer may besubsequently cut, compressed, densified, or otherwise shaped to form anouter layer having a stem portion and a sound attenuating portion.

An earplug and a method of making an earplug describe herein providesseveral benefits. The earplug described herein may be comfortablypositioned in the ear canal of a user to provide a desired level ofhearing protection, and the presence of a stiffer elongate core promoteshygiene by eliminating the need to roll down a sound attenuating portionprior to insertion. The method described herein allows an earplug to beefficiently manufactured. An earplug having an outer layer bonded,directly or indirectly, to an elongate core as described hereineliminates the cost and complexity of an additional step of joining arigid component to a sound attenuating component required of many priorpush-in type earplugs. The elongate core and outer layer can bethermally bonded without the need for an additional adhesive oradditional assembly step.

The present invention has now been described with reference to severalembodiments thereof. The foregoing detailed description and exampleshave been given for clarity of understanding only. No unnecessarylimitations are to be understood therefrom. It will be apparent to thoseskilled in the art that many changes can be made in the embodimentsdescribed without departing from the scope of the invention. Thus, thescope of the present invention should not be limited to the exactdetails and structures described herein, but rather by the structuresdescribed by the language of the claims, and the equivalents of thosestructures. Any feature or characteristic described with respect to anyof the above embodiments can be incorporated individually or incombination with any other feature or characteristic, and are presentedin the above order and combinations for clarity only.

What is claimed is:
 1. An article comprising: an elongate corecomprising a first material and having first and second ends and anouter major surface; and an outer layer comprising a second material andcovering at least a portion of the outer major surface of the elongatecore, the second material comprising an unactivated expandable spherefoaming agent and an unactivated chemical foaming agent; wherein theunactivated foaming agents may be activated to increase the volume ofthe outer layer, and the core exhibits a stiffness that is greater thana stiffness of the outer layer.
 2. The article of claim 1, wherein thesecond material comprises between 0.5% weight and 3% weight of anunactivated chemical foaming agent.
 3. The article of claim 1, whereinthe second material comprises between 0.5% weight and 9.5% weight of anunactivated expandable sphere foaming agent.
 4. The article of claim 1,wherein the second material comprises between 90% and 99% by weight ofstyrene-ethylene-butylene-styrene (SEBS).
 5. The article of claim 1,wherein a channel extends at least partially through the elongate corebetween the first and second ends in a longitudinal direction.
 6. Thearticle of claim 1, wherein the outer layer has an outer diameterbetween 2.5 mm and 6.5 mm.
 7. The article of claim 1, wherein theelongate core has an outer diameter between 1.5 mm and 3.5 mm.
 8. Thearticle of claim 1, wherein the elongate core has a length between thefirst and second ends that is greater than 1 m.
 9. An articlecomprising: a substrate comprising a first material and having a majorsurface; and an outer layer comprising a second material and covering atleast a portion of the major surface of the substrate, the secondmaterial comprising an unactivated expandable sphere foaming agent andan unactivated chemical foaming agent; wherein the unactivated foamingagents may be activated to increase the volume of the outer layer, andwherein the substrate exhibits a stiffness that is greater than astiffness of the outer layer.
 10. The article of claim 9, wherein thesecond material comprises between 0.5% weight and 3% weight of anunactivated chemical foaming agent.
 11. The article of claim 9, whereinthe second material comprises between 0.5% weight and 9.5% weight of anunactivated expandable sphere foaming agent.
 12. The article of claim 9,wherein the second material comprises between 90% and 99% by weight ofstyrene-ethylene-butylene-styrene (SEBS).